Rolling mill gauge control method and apparatus including temperatureand hardness correction

ABSTRACT

The roll openings of the respective roll stands of a tandem hot steel strip rolling mill are controlled in relation to the measured temperature of an approaching present workpiece, which is similar to a previous workpiece, and which measured temperature of the present workpiece is compared to the weighted average temperature of previous similar workpieces. In addition the workpiece hardness as indicated by the measured lock on roll force for the present workpiece and compared to the weighted average of the lock on roll forces of previous similar workpieces is used for control purposes. The automatic gauge control system calculates the screwdown movement correction required for correction of the roll opening of each roll stand in relation to the expected per unit change in stand roll force for at least one of these comparisons. The control system operates the mill screwdowns in accordance with these calculated screwdown movement corrections.

United States Patent [191 Smith, Jr.

[ ROLLING MILL GAUGE CONTROL METHOD AND APPARATUS INCLUDING TEMPERATUREAND HARDNESS CORRECTION 1 [75] Inventor: Andrew W. Smith, Jr.,Pittsburgh,

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Nov. 6, 1972 [2]] Appl. No.: 303,723

I [52] US. Cl. 72/9, 72/13 [51] Int. Cl B2lb 37/10 [58] Field of Search72/8, 6, 13

[56] 7 References Cited UNITED STATES PATENTS 3.111.046 11/1963 Koss eta1. 72/15 X 3,186,201 6/1965 Ludbrook ct al. 3,253,438 5/1966 Stringer3.568.637 3/1971 Smith, Jr 3,628.358 12/1971 Fapiano 3,691,801 9/1972Gillstrom 72/9 i 3,820,366 ].June 28,1974

Primary ExaminerMilton S. Mehr Attorney, Agent, or Firm-R. G. Brodahl [57] ABSTRACT The roll openings of the respective roll stands of a tandemhot steel strip rolling mill are controlled in relation to the measuredtemperature of an approaching present workpiece, which is similar to aprevious workpiece, andwhich measured temperature of thepresentworkpiece is compared to the weighted average temperature ofprevious similar workpieces. In addition the workpiece hardness asindicated by the measured lock on roll force for the present workpieceand compared to the weighted average of the lock on roll forces ofprevious similar workpieces is used for control purposes. The automaticgauge control system calculates the screwdown movement correctionrequired for correction of the roll opening of each roll stand inrelation to the expected per unit change in stand roll force for atleast oneof these comparisons;

The control system operates'the mill screwdowns in accordance with thesecalculated screwdown movement corrections.

15 Claims, 5 Drawing Figures SCR EWDOWN POSITIONING CONTROL 2 SCREWDOWNPOSITION DE TECTOR SCREWDOWN POSITIONING CONTROL s l'c POSITION DETECTORCF OP H SH :AR

I MILL ENTRY SIDE L SIDE TEMPERATURE iGUARDS 1 GUARDS] nsrecroa 37 @T 53SI spar-:0

B TENSION B TENSION CONTROL CONTROL INFORMATION .11

lNPUT AUTOMATIC 1 DEVICES GAUGE CONTROL SYSTEM OPERATOR STATION DISPLAYururs.

CONTROL PANEL E %E I ROLLING MILL GAUGE CONTROL METHOD AND APPARATUSINCLUDING TEMPERATURE AND I-IARDNESS CORRECTION CROSS REFERENCE TORELATED APPLICATIONS Reference is made to the following previously filedand related patent applications which are assigned to the presentassignee:

Ser. No. 215,747, filed Jan. 6, 1972 and entitled Gauge Control MethodAnd Apparatus Including Workpiece Plasticity Determination For MetalRolling Mills, by A. W. Smith and R. Q. Fox.

Ser. No. 215,749, filed Jan. 6, 1972 and entitled Gauge Control MethodAnd Apparatus Including Workpiece Gauge Deviation Correction for MetalRolling Mills, by A. W. Smith and R. 0. Fox.

Ser. No. 215,743, filed Jan. 6, 1972 and entitled Gauge Control MethodAnd Apparatus For Metal Rolling Mills, by A. W. Smith and R. Q. Fox.

Ser. No. 031,842, filedApr. 30, 1970 and entitled Gage Control SystemFor I-Iot Rolling Mills, by R. B. Gillstrom.

Reference is made to the following concurrently filed and related patentapplications which are assigned to the present assignee:

Ser. No. 303,721, filed Nov. 6, 1972 entitled Rolling Mill Gauge ControlIncluding Entry Gauge Correction, and filed by A. W. Smith and R. Q.Fox.

Ser. No. 303,725, filed Nov. 6, 1972 entitled Rolling Mill Gauge ControlIncluding Speed Correction, and filed by R. Q. Fox. 1

Ser. No. 303,724, filed Nov. 6, 1972 entitled Rolling Mill Gauge ControlIncluding X-ray Correction, and filed by R. Q. Fox.

Ser. No. 303,722, filed Nov.v 6, 1972 entitled Rolling Mill GaugeControl Including Feedback Correction, and filed by R. Q. Fox and D. J.Emberg.

Ser. No. 303,723, filed Nov. 6, 1972 entitled Rolling Mill Gauge ControlIncluding Plasticity Determination and filed by R. Q. Fox.

BACKGROUND OF THE INVENTION The present invention relates to workpiecestrip metal tandem rolling mills and more particularly to roll forcegauge or thickness control systems and methods used in operating suchrolling mills.

In the operation of a metal or steel reversing or tandem rolling mill,the unloaded roll opening and the speed at each tandem mill stand or foreach reversing mill pass can be set up by the operator to producesuccessive workpiece (strip or plate) reductions resulting in deliveredwork product at the desired thickness or gauge. 1

Since the operator provided initial setup conditions, or the initialrollopening settings provided by an associated computer control systemoperative with model equation information to calculate the setupscrewdown schedules for the rolling mill, can be in error and since inany event certain mill parameters affect each stand loaded roll openingduring rolling and after setup conditions have been established, a standautomatic gauge control system is desired if it is necessary that thestand delivery gauge be closely controlled. Thus, at the present stateof the rolling mill art, and particularly the steel rolling mill art, astand gauge control system is normally used for a reversing mill standand for predetermined stands in tandem rolling mills.

More particularly, the well known gaugemeter or roll force system hasbeen widely used to produce stand gauge control in metal rolling millsand particularly in tandem hot steel strip rolling mills and reversingplate mills where experience has demonstrated that roll force control isparticularly effective. Earlier publications and patents, such as anarticle entitled Installation and Operating Experience with Computer andProgrammed Mill Controls by M. D. McMahon and M. A. Davis in the 1963Iron and Steel Engineer Year Book at pages 726 to 733, an articleentitled Automatic Gage Control for Modern Hot Strip Mills by J. W.Wallace in the Dec. 1967 Iron and Steel Engineer at pages to 86', US.Pat. No. 3,561,237 issued Feb. 9, 1971 to Eggers et al. and US. Pat. No.2,726,541, issued Dec. 13, 1955 to R. B. Sims, describe the theory uponwhich operation of the roll force and related gauge control a systems isbased. Attention is also called to US. Pat. No. 3,568,637 issued Mar. 9,1971, US. Pat. Nos.

3,574,279 and 3,574,280 issued Apr. 13, 1971, and I US. Pat. No.3,600,920 issued Aug. 24, 1971 to A. W. Smith which relate to roll forceautomatic gauge control systems. In referencing prior art publicationsor patents as background herein, no representation is made that thecited subject matter is the best prior art.

Briefly, the roll force gauge control system uses Hookes law incontrolling the screwdown position at a rolling stand,i.e. the loadedroll opening under workpiece rolling conditions equals the unloaded rollopening or screwdown position plus the mill spring stretch caused by theseparating force applied to the rolls by the workpiece. To embody thisrolling principle in the roll force gauge control system, a load cell orother force detector measures the roll separating force at eachcontrolled roll stand and the screwdown position is controlled tobalance roll force changes from a reference value and thereby hold theloaded roll opening at a substantially constant value. The followingwell known formula expresses the basic roll force gauge controlrelationship:

h=S0+F.K.

position signals to control the screwdown position and hold thefollowing equality:

AS -AF-K where AF measured change in roll force from an initial force AS=controlled change in screwdown position from an initial screwdownposition. Afterthe unloaded roll opening setup and the stand speed setupare determined such as by the mill operator for a particular workpiecepass or series of passes, the rolling operation of an actual workpieceis begun and the screw-downs are controlled to regulate the workpiecedelivery gauge from the reversing mill stand or from each roll forcecontrolled tandem mill stand. By satisfying Equation (2), and theassumptions implicit in Equation l the loaded roll opening h in Equation(1) is maintained constant or nearly constant. 2 As the head end of theworkpiece strip enters each roll stand of the mill, the lock-onscrewdown position and the lock-on roll separating force are measured toestablish what strip gauge should be maintained out of that roll stand.As the strip rolling operation proceeds, the roll stand separating forceand the roll stand screwdown position values are monitored and anyundesired change in roll separating force is detected and compensatedfor by a corresponding correction change in screwdown position. Thelock-on gauge LOG is equal to the lock-on screwdown LOSD plus thelock-on force LOF multiplied by the mill stand spring modulus K. Theworkpiece strip delivery gauge G leaving the roll stand at any timeduring the rolling operation is in accordance with above equation (1)and is equal to the unloaded screwdown position SD plus the rollseparating force F multiplied by the mill spring modulus K. The gaugeerror is derived by subtracting the lock-on gauge from the deliverygauge. The following .Equa: tions 3, 4 and 5 set forth theserelationships.

(4) G LOG GAUGE ERROR SD LOSD (FLOF)*K (5) One mill condition which cancause gauge error is the rolling of a present workpiece having adifferent temperature or hardness when compared to a previous workpieceof similar grade and/or gauge classification.

There are cited several prior art publications and patents in theprosecution file of the above-referenced Gillstrom patent applicationthat are. related to the measurement or workpiece temperature for theimprovement of the workpiece rolling operation.

A digital computer system can be employed to make the screwdowncorrection movement determinations as well as to perform other millcontrol functions. The digital computer employs a programming systemincluding an automatic roll force gauge control program or AGC programwhich is executed at predetermined intervals to calculate the desiredscrewdown movement required at each roll force gauge controlled standfor gauge error correction including that related to roll force errordetection at that stand. Screwdown movement for correcting roll forceerror is made on the basis of calculations which use selected workpieceplasticity and mill spring constant values stored in data tables in thecomputer system memory or otherwise determined by the digital computersystem.

' There is disclosed in the above-referenced previously filed patentapplication Ser. No. 215,743 the logic flow chart of an illustrativeautomatic gauge control suitable for operation with the temperature andforce correction operation of the present invention. It should bereadily understood by persons skilled in this art that the presentinvention is also suitable for operation with other well known automaticgauge control systems for controlling the delivery gauge of a workpiecestrip passed through the roll stands of a rolling mill.

A background teaching of stored program digital computer systemoperation can be found in a book entitled Electronic Digital Systems byR. K. Richards and published in l966 by John Wiley and Sons.

Amore detailed description of computer programming techniques inrelation to the control of metal rolling mills can be found in anarticle in the Iron and Steel Engineer Yearbook for 1966 at pages 328through 334 entitled Computer Program Organization for an AutomaticallyControlled RollingMill by John S. Deliyannides and A. H. Green, and inanother article in the Westinghouse Engineer for Jan. 1965 at pages 13through 19 and entitled Programming for Process Control by P. E. Lego.

SUMMARY OF THE lNVENTlON At least one of a different workpiecetemperature or a different workpiece hardness is detected in relation tothe established pattern of previously rolled similar workpieces. This isdone in relation to temperature by comparing the measured head endtemperature CST of each new workpiece as measured at the crop shearahead of the finishing mill stands, with the measured and average valueof the head end temperature ACST of the previously rolled similarworkpieces. A new workpiece, similar in gauge class and grade class topreviously rolled workpieces, that is hotter or colder than thepreviously established average crop shear temperature ACST, will requirean adjustment to be made in the operator scheduled roll opening beforethe new workpiece enters the mill stands.

This is done in relation to hardness by measuring the head end or lockon roll force LOF(I) of this same new workpiece, as measured in thefirst operating stand of the rolling mill, and ratio comparing this withthe established average ALOF(I) for lock on roll force measurements forsimilar previous workpieces. A new present workpiece that is harder orsofter than the average hardness of these previous workpieces, asindicated by the measured lock on roll force at stand one, requires anadjustment in the roll opening of each subsequent stand in the rollingmill, perhaps not adjusting the sec ond stand because of available timefor moving the screws to make the change in the second stand rollopening setting.

The initial roll opening for each stand is provided as an operator inputwithin a provided schedule of these roll openings to establish the rollopening setting for each stand.

The determined correction is in the form of a per unit change in rollforce for each stand, so the adjustment for the screwdown or rollopening setting for each stand is calculated by taking the product ofeither one of a temperature or force correction, TCF for temperaturedifference determined correction factor or FCF for the hardnessdifference determined correction factor, times the normal or averagelock on force ALOF (N) for that stand (N) times the known stand millspring constant K(N) to determine how much the change or the adjustmentshould be in relation to the operator scheduled stand (N) roll openingSDREF(N) to compensate for the expected per unit change in roll force atstand (N), due to either one or both of the sensed temperaturedifference of the new workpiece and the sensed different hardness inrelation to the new workpiece.

In both the operation of the temperature determined correction TCF andthe force determined correction FCF, the actual correction establishedis in the form of the expected per unit change in the stand roll force.Thusly, the corrected screwdown CSD(N) for each stand (N) roll openingis calculated using the proper one of the following equationrelationships:

CSD(N) SDREF(N) ALOF(N) TCF K(N) 6 CSD(N) SDREF(N) e ALOF(N) FCF K(N) 7)where equation (6) is used to determine the temperature differencedetermined correction and where equation (7) is used to determine thehardness difference determined correction. The average or normal lock onforce ALOF(N) for each stand (N) as used in the above equations isdetermined by the following relationship ALOI-(N) =[ALOF(N) WF+LOF(N)]/WF+1 s) ,where the new averagelock on force ALOF(N) for each ofthe roll stands is determined each time that the head end of a newworkpiece, having a similar grade class and similar gauge class toprevious rolled workpieces, enters the first operating roll stand (I).This new average lock on force ALOF( N) is determined for each rollstand by equation (8) in relation to the previous value of this averagelock on force multiplied by a predetermined weighting factor WF plus themeasured lock on roll force LOF(N) for the head end of the presentworkpiece and divided by the weighting factor WF plus one. The weightingfactor WF used in equation (8) is determined each time the stands of therolling mill are preset with a schedule of roll opening settings for therespective stands of the rolling mill, such as would occur prior to theentry of another workpiece as compared to the last workpiece to passthrough the stands of the rolling mill. This weighting factorisdetermined by the following equation relationship:

where the new weighting factor for the next workpiece is equal to theold weighting factor, for a given operator determined schedule inrelation to the number of workpieces similar to the next workpiece inrelation to grade class and gauge class that have previously passedthrough the stands of the rolling mill in accordance with this sameoperators schedule for the roll opening settings of the respectivestands, plus one. This new weighting factor may then be limit checked,with a TCF (ACST- CST) TK where this temperature correction factor isdetermined each time the head end of a workpiece passes by thetemperature measurement device, for example a pyrometer located adjacentthe position of the crop shear, ahead of the finishing mill stands. Thetemperature correction factor TCF is determined in relation to thedifference between the average of the measured temperatures ACST of therespective previous workpieces passing by the temperature sensingposition and the measured temperature CST the present workpiece at thesensing position location, with that temperature difference then beingmultiplied by a provided constant TK which may have a typical value of0.002 per unit correction per degree F. This temperature correctionfactor TCF is then limited to a value between +0.10 and 0.05 before'itis utilized.

The hardness related force correction factor FCF utilized in equation(7) is determined by the following relationship:

FCF= [LOF(I)]/ALOF(I) l where this force correction factor is determinedeach time a present workpiece strip enters the first operating stand(I), and if desired this operation may be limited to stand (I), beingthe first stand; The force correction factor FCF is determined inrelation to the lock on roll force LOF(I) at stand (I) for the presentworkpiece being divided by the average lock on roll force ALOF(I) atstand (I) for the previous similar workpieces, with that quotient thenbeing reduced by one. The force correction factor may then be limited toa value between +0.10 and 0.05 before it is utilized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. lshows a schematic diagram of atandem hot steel striprolling mill and an automatic gauge controltherefor arranged for operation in accordance with the presentinvention;

FIG. 2 shows an illustrative logic flow chart of the weighting factor WFdetermination in accordance with the present invention;

FIG. 3 shows an illustrative logic flow chart of the stand averagelock-on roll force ALOF( N) determination program;

FIG. 4 shows an illustrative logic flow chart of the temperaturedifference corrected screwdown reference determination and the averagelock on rollforce determination; and

FIG. 5 shows an illustrative logic flow chart of the hardness, correctedscrewdown reference determination.

GENERAL DESCRIPTION OF THE GAUGE CONTROL SYSTEM AND ITS OPERATION Thereis shown in FIG. 1 a tandem hot strip steel finishing mill 11 operatedwith improved gauge control performance by a process control System13 inaccordance with the principles of the invention. Generally, however, theinvention is applicable to various types of mills in which roll forcegauge control is employed. Thus, the invention can be suitably adaptedfor application in hot steel plate reversing and other rolling mills.

The tandem mill 11 includes a series of reduction rolling stands withonly two of the stands S1 and S6 shown. A workpiece 15 enters the mill11 at the entry end in the form of a bar and it is elongated as it istransported through the successive stands to the delivery end of themill where it is coiled as a strip of a downcoiler 17. The entry barwould be of known steel grade classification and it typically would havea thickness of about 1 inch and a width within some limited range suchas inches to 80 inches. The delivered strip would have approximately thesame width and a delivery gauge or thickness classification based uponthe production order for which it is intended.

In the reduction rolling process, the successive stands operate atsuccessively higher speeds to maintain proper workpiece mass flow. Eachstand produces a predetermined reduction or draft such that the totalmill draft reduces the entry bar to strip with the desired gauge orthickness.

Each stand is conventionally provided with a pair of backup rolls 19 and21 and a pair of work rolls 23 and 25 between which the workpiece 15 ispassed. A large DC drive motor 27 is controllably energized at eachstand to drive the corresponding work rolls at a controlled speed.

As previously described, for a given stand the sum of the unloaded workroll opening and the mill stretch substantially defines the workpiecegauge delivered from any particular stand in accordance with Hookes law.To vary the unloaded work roll opening at each stand, a pair ofscrewdown motors 29 (only one shown 'at each stand) position respectivescrewdowns 31 (only one shown at each stand) which clamp againstopposite ends of the backup rolls and thereby apply pressure to the workrolls. Normally, the two screwdowns 31 at a particular stand would be inidentical positions, but they can be located in different positions forstrip guidance during threading, for flatness or other strip shapecontrol purposes or possibly for other purposes.

A conventional screwdown position detector or encoder provides anelectrical representation of screwdown position at each stand. Toprovide an absolute correspondence between the screwdown position andthe unloaded roll opening between the associated work rolls, a screwdownposition detection system which includes the screwdown position detector33 can be calibrated from time to time.

Roll force detection is provided at each of predetermined stands by aconventional load cell 35 which generates an electrical analog signal.At the very least, each roll force controlled stand is provided with aload cell 35 and in many cases stands without roll force gauge controlwould also be equipped with load cells. The number of stands to whichroll force gauge control is applied is predetermined during the milldesign in accordance' with cost-performance standards, and increasinglythere is a tendency to apply roll force gauge control to all of thestands in a tandem hot strip steel. mill. In the present case, a rollforce gauge control system is, assumed to be employed at each of thestands.

Conventional motorized sideguards 37 arelocated at predetermined pointsalong the mill length. The sideguards 37 are operated during mill setupon the basis of the widths of the upcoming workpiece 15 thereby .ancePUI'POSCS.

The process control system 13 provides automatic control for theoperation of the tandem mill 1] as well as may be desired for associatedproduction processes (not indicated) such as the operation of a roughingmill. Preferably, the process control system 13 comprises an automaticgauge control system 39 which can include a programmed process controldigital computer, and which is interfaced with the various mill sensorsand the various mill control devices to provide control over many of thevarious functions involved in operating the tandem mil] 11. According touser preference, the control system 13 .can also include conventionalmanual and/or automatic analog controls for backup operation inperforming preselected mill functions.

The automatic gauge control system 39 can include a finishing millon-line roll-force gauge control digital computer system, such as aProdac 2000(P2000) sold by Westinghouse Electric Corporation. Adescriptive book entitled Prodac 2000 Computer Systems Reference Manualhas been published in 1970 by Westinghouse Electric Corporation and madeavailable for the purpose of describing in greater detail this digitalcomputer system and its operation.

A digital computer processor can be associated with well knownpredetermined input systems typically including a conventional contactclosure input system which scans contact or other signals representingthe status of various process conditions, a conventional analog inputsystem which scans and converts process analog signals, and operatorcontrolled and other information input devices and systems such as papertape teletypewriter and dial input systems. It is noted that suitableinformation input devices 41 are generally indicated by a single blockvin FIG. 1 although different input devices can and typically would beassociated with the automatic gauge control system 39. Various kinds ofinformation are entered into the gauge control system through the inputdevices including, for example, desired strip delivery gauge andtemperature, strip entry gauge and width and temperature (by entrydetectors if desired), grade of steel being roller, plasticity tables,suitable hardware oriented programs and control programs for theprogramming system, and so forth.

The contact closure input'systems and the analog input systems interfacethe automatic gauge control or AGC system 39 with'the process throughthe medium of measured or detected .variables. The present invention islargely involved in the functioning of an automatic gauge controlsystem, which in one typical invention application, various mill signalsare applied to the AGC input systems. These mill signals include thefollowing: v i

l. A roll force signal from the load cell 35 at each stand proportionalto stand roll separating force for use in roll force gauge control.

2. Screwdown position signals generated by the respective detectors 33at thestands for use in roll force gauge control.

3. Screwdown motor speed signals generated by respective tachometers 49at the stands for use in programmed regulation.

4. Stand speed signals generated by respective tachometers 43, with thespeed signal used for calculation of acceleration compensation and forcalculation of time delays in monitor operation. I

5. A gauge deviation signal from an X-ray gauge 47 at the delivery endof the mill for programmed monitor gauge control through the roll forcecontrol. 1

6. An entry temperature signal from a mill entry temperature detector orpyrometer 45; the mill entry temperature for the head end of eachworkpiecelS is stored.

- 7. Width signals supplied by sideguard follow potentiometers for millspring constant calculations, etc.

It is noted at this point in the description, that the measured head endroll force is. stored and used as a reference for roll force gaugecontrol functioning at the respective stands if the AGC system is in thelock-on mode of roll force operation.

A contact closure output system would normally be associated with adigital computer,-and inthe operation of the AGC output system, variouscontrol devices are operated in response to control actions calculatedor determined by the AGC system 39.

To effect determined control actions, controlled devices are operateddirectly by means of output system contact closure or by means of analogsignals derived from output system contact closures through a digital beassociated with the outputs of the AGC system 39- in order to keep themill operator generally informed about the mill operation and in orderto signal the operator regarding an event or alarm condition which mayrequire some action on his part. The printout systems are also used tolog mill data.

' Generally, the AGC system 39 uses Hookes law to determine the totalamount of screwdown movement required at each roll force controlledstand at the calculating point in time for roll force and gauge errorcorrection, i.e. for loaded roll opening and stand delivery gaugecorrection to the desired value. The calculation defines the totalchange in the unloaded roll opening required to compensate for a newmill stretch value or other roll force and gauge error causingcondition. The predicted corrective screwdown position change value isemployed by the AGC system to define the screwdown motor position-timeprofile to be followed in making the corrective screwdown movement.

During rolling operation, the on line gauge control system operates thestands to produce strip product having desired gauge. On line gaugecontrol is produced by the roll force gauge control loops at the standsand the previously noted screwdown monitor gauge control system.

In the monitor system, the X-ray gauge 47 produces the previouslyindicated X-ray deviation signal which indicates the difference betweenactual strip delivery thickness and desired or target strip deliverythickness. in other cases, it may be desirable to employ an absolutethickness measurement X-ray gauge signal to form a basis for monitorcontrol actions or, more generally, for screw-down position offsetcontrol actions. I

To effect on line gauge control in the closed loops, the AGC systemoperates on the screwdown position detector and load cell signals fromeach stand as well as the X-ray gauge deviation signal to determine thecontrol actions required for producing desired strip delivery gauge.Screwdown motor speed is in this invention also applied to the AGCsystem 39 in order to provide for desired screw-down positioningcontrol. In effecting control operations, the AGC system can employ adigital computer including an AGC programming system which forms a partof the total programming system for the AGC system 39. The AGCprogramming system could include programs oriented to controlling theAGC system hardware and programs oriented to developing the desiredcontrol actions.

It is generally known and understood by persons skilled in thisparticular art of applying a digital computer control system that acombined hardware and software process control system comprises aspecial purpose extended control computer machine, and is provided whena general purpose computer is operated under the control of one or moresoftware instruction programs. Such a process control system can bebuilt if desired using hardware or wired logic programming in relationto the functional steps set forth in the flow charts, in view of therecognized general equivalence of a software programming-embodiment anda hardware programming embodiment and a hardware programming embodimentof substantially the same control system. However, when an involvedindustrial application such as here described becomes somewhat complex,the economics tend to favor the software approach due to the greaterexpense and lack of flexibility when hardware logic circuits, such aswell known NOR logic circuits, are wired together to provide the desiredcircuit arrangement built up of such logic circuits to perform thesequential program steps set forth in the illustrated flow charts.

DESCRIPTION OF PREFERRED EMBODIMENT The AGC system is operative todetect present workpieces that are a different temperature or adifferent hardness in relation to previous similar workpieces and toadjust the roll opening of each stand as desired. This is done bycomparing the temperature of the head end of the present workpiece as itpasses the crop shear and approaches the mill with the temperaturemeasurements on previous similar workpieces. A present work piece causesadjustments in the roll openings on the subsequent roll stands(excluding the second roll stand because of a lack of available time tomake the desired correction). This gauge control method does not requirea force prediction for each roll standsince the normal roll force isestablished from roll force measurements from preceding similarworkpieces. No roll opening. correction is made in relation to eitherroll force or present workpiece temperature measurements on the firstworkpiece of a new schedule.

In both the temperature'correction operation and the force feed forwardhardness correction operation, the roll opening correction is in theform of an expected per unit change in the stand roll force so thecorrection for each roll opening is calculated by taking the product ofthe correction, the normal roll force for that stand and the known millspring constant to find how much the roll opening for a given standshould be changed to compensate for the expected change in roll force inrelation to the present workpiece.

The required change or correction to be made in relation to theoperation provided roll opening or screwdown setting for each roll stand(N) which it is desired be corrected can be determined in relation tothe temperature difference by the relationship:

ASDUV) =ALOF(N) TCF K(N) weighting factor WF is set equal to zero andthe program operation ends. lf at step 100 a new schedule is notprovided, then at step 104 the weighting factor for the presentworkpiece is set equal to the previous weighting factor plus one. Atstep106 a determination is made to see if the weighting factor. is greaterthan five, and if so, at step 108 the weighting factor is limited tofive.

In FIG. 3 there is shown a flowchart to illustrate the determination ofthe average lock-on roll force for a given roll stand N, for N equal tostand one through N equal to the last stand. Thusly, if the mill setupis for a new schedule for this present workpiece, the weighting factorWF is set to zero; otherwise, the weighting factor is increased by onebut limited to five. Each time a present workpiece strip enters a rollstand N, the lockon roll force of that stand N is measured for use inthe roll force gauge control system. At step 120'there is determined foreach roll stand (N) the weighted average lock-on roll force ALOF(N) foreach stand N. For the first workpiece of a new schedule, the weightingfactor WF is zero and the average lock-on force ALOF is then set equalto the actual lock-on force LOF measured on the particular firstworkpiece. On subsequent similar workpieces, the weighting factor'WFincreases in value up to a maximum of five and a weighted average ornormal lock-on roll force level ALDF N) is establishedfor each stand Nin accordance with the formula relationship shown at step 120.

In FIG. 4 there is shown a flowchart to illustrate the determination ofthe weighted average crop shear temperature ACST in relation to previoussimilar workpieces. At step a check is made to see if the weightingfactor WF is now set at zero. If so, the program advances to step wherea determination is made of the average crop shear temperature ACST asbeing equal to the measured crop shear temperature CST for the presentworkpiece, since the weighting factor WF is now equal to zero toindicate that a new rolling schedule is underway and the present-workpiece is the first workpiece of a given grade classification andgauge classification to be rolled under that new schedtile. The asteriskindicates a multiplication function. If the weighting factor for thepresent workpiece is not zero, at step 132 the difference in temperaturebetween the average crop shear temperature ACST and the presentworkpiece temperature CST is converted into an expected per unit changein roll force through multiplying by the predetermined temperatureconstant TK, which has a preselected value of about 0.002 per unit forcechange per degree Fahrenheit. The temperature correction factor TCF islimited to a range between positive 0.1 and negative 0.05 in steps 134through 140. At step 142 the stand (N) screwdown reference SDREFismodified to compensate for an expected change in roll force that isestablished in relation to the average roll force ALOF and thetemperature correction factor TCF. This change in roll force isconverted into an adjustment in the operator provided roll openingsetting SDREF(N) by multiplying by the stand (N) mill spring modulusK(N). The corrected screwdown setting CSD(N), is then used as a newposition setting reference value for the stand (N) roll opening positionregulator. The program then goes to step 135 where the determination ismade of the average crop shear temperature ACST in relation to all thesimilar workpieces now considered, up to a maximum of the last five suchworkpieces.

In FIG. 5 there is shown a flowchart to illustrate an operation thatoccurs when the head end of the present workpiece enters the firstoperative roll stand Al, such as stand one, to determine the hardnesscorrected screwdown setting CSD(N) for stand (N). This determination isdone in relation to each of the operative roll stands after the firstoperative roll stand, such that N equals I 2 to N equals the last stand;because of the time requirements for effecting the desired correction inthe screwdown setting of the roll stand next following the firstoperative roll stand, it may be desired not to attempt to make acorrection in relation to that next following roll stand, and for thisreason N has been selected as -N equals 1 2, where stand I is the firstoperative roll stand. At step a check is made to see if the weightingfactor WF is now'set at zero, to indicate that a new operator providedschedule is beginning with the present workpiece. If so, the programends.

. If the weighting factor WF is not now set at zero, at step 152 a rollhardness correction factor FCF is determined as the ratio of themeasured lock-on force CSD(N), for each of the subsequent roll stands Nequals I 2 through N equals TI-IE the last stand, is determined inaccordance with the relationship of the above equation (8). 7

If desired, the calculation of the force correction factor FCF by theoperation illustrated by the flowchart of FIG. does not have to belimited to the lock-on force relationship for the first operating rollstand, but instead this calculation can be performed using the lockonforce relationship for one or more other subsequent stands to establisha correction for one or more stands subsequent to that other stand.

When the head end of the present workpiece passes under the temperaturemeasuring device, such as a pyrometer located adjacent the crop shear,the operation illustrated by FIG. 5 can take place to determine thetemperature related corrected screwdown setting CSD(N) for each of rollstands one to the last stand. When the present workpiece subsequentlyenters the first operative stand I, the operation illustrated by FIG. 5can take place to determine a subsequent and further hardness relatedscrewdown setting correction CSD(N) for each of roll stands I 2 to thelast stand.

Either one or both of these program operations may be used as desired bythe operator. The temperature difference correction factor TCF has theadvantage of making the screwdowncorrection of all the stands of therolling mill before the present workpiece enters, but an accuratepresent workpiece temperature measurement is not easy to maintain. Sincea change in similar workpiece temperature measurements is being used forthe temperature difference related correction, it is more reliable thana control system operation that would require an absolute temperaturemeasurement ability. The hardness related force feed forward correctionfactor FCF is easier to establish, and it can be used alone or inconjunction with the temperature related correction.

The routine gauge controlling improvement of the mill roll standscrewdown setups to accommodate the normal pieces within the normaltemperature and hardness patterns is done by other systems, such as aconventional roll force AGC or the schedule calculation adaptive controlsystem utilizing process model equations. Such improvements would bereflected in modified values of the roll opening reference, SDREF, foreach stand. The here described control operation is provided to detectthe temperature and hardness differences between a particular presentpiece and the normal patterns as established by the rollingof previousworkpieces. The most common cause for such differences is aninterruption in the movement of a given workpiece through the roughingmill and across the transfer table to the finishing mill. Such a timedelay results in a loss of heat, so most screwdown setting correctionsof any magnitude will more likely be in the dithe pyrometer located infront of the shear, and in accordance with FIG. 3,the control systemdetermines the deviation of the temperature of the present workpiecefrom the temperature of the workpieces preceding it. This temperaturedeviation is used to calculate the expected change in rolling force foreach stand of the rolling mill.

The expected hardness related change in rolling force is used, inconjunction with the mill spring constant, in accordance with FIG. 4, tocalculate the required corrective change in roll opening for each standthat is necessary to produce on-gauge strip. As the previous strip fallsout of each stand. the screws for that stand are positioned to correctfor any hardness correction and any temperature correction.

If the operator chooses to input the temperature deviation manually, theroll opening correction can be obtained from a predetermined table ofvalues. This procedure ensures that the manual input produces apredictable response each time it is used.

The temperature correction operation is initiated by a hot metaldetector located near the shear. If automatic temperature correctionoperation is selected, the temperature is read on the first scan afterthe present workpiece passes under the pyrometer at the shear. If thisworkpiece is for a different gauge class of product than the lastworkpiece, the program exits without taking action. Otherwise, theprogram calculates how much the temperature of the present workpiecediffers from the temperature of the previous workpiece in the similargauge class and then uses this deviation in temperature-to predict thechange in roll force which can be expected. This calculation assumesthat the roll force is a'linear function of temperature. The operatorshould determine empirically the actual slope of the relationshipbetween roll force and temperature.

The program limits the predicted force change to no more than +20percent or lO percent. It then corrects the set-up of each stand rollopening to handle the offtemperature present workpiece. The correctionto the set-up is calculated as a change to the previous set screwposition. The change in screwdown is calculated by multiplying theexpected change in roll force by the mill spring constant.

If there is a strip in the stand, the program sets flags to signal theAGC program to include temperature compensation with the head endcorrection. Otherwise, it bids for the screwdown positioning operationto correct the set-up immediately.

GENERAL DESCRIPTION OF INSTRUCTION PROGRAM LISTING In the Apendix thereis included an instruction program listing that has been prepared tocontrol the roll force automatic gauge control operation of a tandemrolling mill in accordance with the here-disclosed con trol system andmethod. The instruction program listing is written in the machinelanguage of the PRODAC P2000 digital computer system, which is sold byWestinghouse Electric Corporation for real time process control computerapplications. Many of these digital computer systems have already beensupplied to customers, including customer instruction books anddescriptive documentation to explain to persons skilled in this art theoperation of the hardware logic and the executive software of thisdigital computer system. This instruction program listing is included toprovide an illustration of one suitable embodiment of the presentcontrol system and method that has actually been prepared. Thisinstruction program listing at the present time has been generallydebugged through the course of practical operation for the real timeautomatic gauge control of a tandem rolling mill. It is well known bypersons skilled in this art that most real time process controlapplication programs contain some bugs or minor errors, and it is withinthe skill of such persons and takes varying periods of actual operationtime to identify and correct the more critical of these bugs.

A person skilled in the art of writing computer instruction programlistings, particularly for an invention such as thepresent roll forceautomatic gauge control system and method for a tandem rolling mill mustgenerally go through the following determinative steps:

Step One Study the workpiece rolling mill and its operation to becontrolled, and then establish the desired controlsystem and methodconcepts.

Step Two Develop an understanding of the control system logic analysis,regarding both hardware and software.

Step Three Prepare the system flowcharts and/or the more detailedprogrammers flowcharts.

Step Four Prepare the actual computer instruction program listings fromthe system flowcharts or from the programmers flowcharts. Thisinstruction program listing included in the Appendix was prepared inrelation to the system flowcharts shown in FIGS; 2 through 5.

What we claim is:

l. A gauge control system for a rolling mill having at least one rollstand operative to reduce the gauge of a plurality of similar workpiecespassed through said rolling mill, said system comprising.

means for determining a difference in the temperature of a present oneof said workpieces in relation to the average temperature of previoussimilar workpieces already passed through said rolling mill,

means operative in relation to said difference for determining atemperature correction factor in relation to a predetermined per .unitchange in roll force multiplier,

means for determining ,a predetermined roll force measurement for saidone roll stand during the passage of said previous similar workpiecesthrough said one roll stand, and I a means for determining a correctedoperation of said one roll stand in relation to said present one of saidworkpieces in accordance with a predetermined relationship between saidcorrection factor and said roll force measurement.

2. The gauge control system of claim 1, with said rolling mill having aplurality of roll stands,

said means for determining the predetermined roll force measurementbeing operative'to determine the average roll force for said one rollstand, and

said means for determining a corrected operation where SDREF(N) is theinitial provided roll opening setting for said one roll stand, whereALDF(N) is the predetermined roll force measurement of said one rollstand, 5 where TCF is the determined correction factor, and

where K(N) is the mill spring modulus for said one rollstand.

4. The gauge control system of claim 1, with said corl0 rected operationbeing determined in accordance with the relationship:

ASD(N) =ALOF(N) TCF K(N) relationship:

where TCF is said temperature related correction factor, I where ACST isthe average temperature of said previous similar workpieces, where CSTis the temperature of said present one of said workpieces, and v I Iwhere TK is the predetermined per unit change in roll force multiplier.I l 6. A gauge control system for a rolling mill having a plurality ofroll stands operative to reduce the gauge of each of a plurality ofsimilar workpieces passed through said rolling mill, said systemcomprising;

means for determining a first predetermined relation- 40 ship betweenthe roll force of a selected roll stand during the passage of a presentone of said workpieces through said selected roll stand and a firstaverage roll force of said selected roll stand during the passage ofprevious similar workpieces through said selected roll stand, means fordetermining a hardness correction factor in accordance with said firstpredetermined relationship, means for determining a second average rollforce of one of said roll stands during the passage of said plurality ofworkpieces through said one roll stand, and means for determining acorrected operation of said one roll stand in accordance with a secondprede-. termined relationship between said hardness correction factorand said second average roll force.

7. The gauge control system of claim 6 with said first predeterminedrelationship being [LOF(I)/ALOF(I)] where LOF (I) is the initial rollforce of said selected 8. The gauge control system of claim 6, with saidfirst predetermined relationship being between the roll force LOF(l) ofa selected roll stand (l) during the passage of said present one of saidworkpieces through said selected roll stand (I) and a first average rollforce ALOF(l) of said selected roll stand (1) during the passage ofprevious similar workpieces through said selected roll stand (I), withsaid hardness correction factor FCF being determined in accordance withsaid first predetermined relationship, and with said corrected operationCSD(N) of said one roll stand (N) being in accordance with a secondpredetermined relationship between said hardness correction factor PCPand a second average roll force ALOF(N). 9. The gauge control system ofclaim 6, with said hardness correction factor FCF being determined bythe relationship where LOF(l) is the initial roll force of said selectedroll stand (I) in relation to said present one workpiece, and

where ALOF(I) is the average roll force of said selected roll stand (I)in relation to said previous similar workpieces.

10. A method of controlling the gauge of a plurality of similarworkpieces passed through a rolling mill having at least one roll stand,the steps of said method comprising:

determining a temperature change between the temperature of a presentworkpiece and the average temperature of the previous similar workpiecespassed through said one roll stand,

determining a temperature correction in relation to said change and apredetermined roll-force relationship to said temperature change,

determining the average roll force of said one roll stand during thepassage of said previous workpieces through that one roll stand, and

deterrning a corrected operation of said one roll stand during thepassage of said present workpiece in accordance with said temperaturecorrection and said average roll force.

11. The method of claim 10, with said determination of said temperaturecorrection being in accordance with TCF= [ACST-CST] TK where TCF is saidtemperature correction,

where ACST is said average temperature,

where CST is said temperature of a present workpiece, and t where TK issaid predetermined roll force relationship to the temperature change.

12. The method of controlling the gauge of a plurality of similarworkpieces of claim 10,

with said temperature change (ACST-CST) being determined between thetemperature CST of a present workpiece and the average temperature ACSTof the previous similar workpieces passed through said one roll stand,

with said temperature correction TCF being determined in relation tosaid change (ACST-CST) and a predetemiined roll force relationship TK tosaid temperature change, and

where TCF is said temperature correction,

where ACST is said average temperature, I

where CST is said temperature of the present workpiece, and

where TK is said predetermined force relationship to the temperaturechange,

and with said corrected operation being in accordance with CSD(N)SDREF(N) ALOF(N) TCF K(N) where CSD(N) is said corrected operation,

SDREF(N) is the inital provided setting of said roll stand (N),

ALOF( N) is a predetermined roll force relationship of said one rollstand (N), and K(N) is the mill spring modulus for said one roll stand(N).

14. A method of controlling the workpiece gauge leaving a rolling millhaving at least one roll stand operative to reduce the gauge of each ofa plurality of similar workpieces passed through said rolling mill, thesteps of said method comprising:

establishing a first predetermined relationship between the roll forceof a selected roll stand during the passage of a present workpiece andthe average roll force of said selected roll stand during the passage ofprevious similar workpieces through said selected roll stand,

establishing a hardness correction in relation to said firstpredetermined relationship,

establishing the average roll force of at least one roll stand duringthe passage of said previous workpieces through said one roll stand, Iestablishing a corrected operation of said one roll stand in accordancewith said hardness correction and said average roll force, andcontrolling the operation of said one roll stand in accordance with saidcorrected operation.

15. The method of claim 14 for controlling the workpiece gauge leaving arolling mill having a plurality of roll stands,

with said first predetermined relationship being established between theroll force LOF(l) of a selected roll stand (I) during the passage ofsaid present workpiece and the average roll force ALOF(I) of saidselected roll stand (1) during the passage of previous similarworkpieces through said selected roll stand,

with the average roll force ALOF(N) being established for at least oneroll stand (N) during the passage of said previous workpieces throughsaid one roll stand,

with said corrected operation CSD(N) of at least said

1. A gauge control system for a rolling mill having at least one rollstand operative to reduce the gauge of a plurality of similar workpiecespassed through said rolling mill, said system comprising. means fordetermining a difference in the temperature of a present one of saidworkpieces in relation to the average temperature of previous similarworkpieces already passed through said rolling mill, means operative inrelation to said difference for determining a temperature correctionfactor in relation to a predetermined per unit change in roll forcemultiplier, means for determining a predetermined roll force measurementfor said one roll stand during the passage of said previous similarworkpieces through said one roll stand, and means for determining acorrected operation of said one roll stand in relation to said presentone of said workpieces in accordance with a predetermined relationshipbetween said correction factor and said roll force measurement.
 2. Thegauge control system of claim 1, with said rolling mill having aplurality of roll stands, said means for determining the predeterminedroll force measurement being operative to determine the average rollforce for said one roll stand, and said means for determining acorrected operation being operative to determine a corrected operationfor said one roll stand in relation to the respective average roll forceof that roll stand.
 3. The gauge control system of claim 1, with saidcorrected operation being determined in accordance with therelationship: CSD(N) SDREF(N)-(ALOF(N) * TCF * K(N)) where CSD(N) is thecorrected roll opening setting for said one roll stand, where SDREF(N)is the initial provided roll opening setting for said one roll stand,where ALDF(N) is the predetermined roll force mEasurement of said oneroll stand, where TCF is the determined correction factor, and whereK(N) is the mill spring modulus for said one roll stand.
 4. The gaugecontrol system of claim 1, with said corrected operation beingdetermined in accordance with the relationship: Delta SD(N) ALOF(N) *TCF * K(N) where -SD(N) is the correction to the roll opening settingfor said one roll stand, where ALOF(N) is the predetermined roll forcemeasurement of said one roll stand, where TCF is the determinedtemperature correction factor, and where K(N) is the mill spring modulusfor said one roll stand.
 5. The gauge control system of claim 1, withsaid correction factor being determined in accordance with therelationship: TCF (ACST-CST) * TK where TCF is said temperature relatedcorrection factor, where ACST is the average temperature of saidprevious similar workpieces, where CST is the temperature of saidpresent one of said workpieces, and where TK is the predetermined perunit change in roll force multiplier.
 6. A gauge control system for arolling mill having a plurality of roll stands operative to reduce thegauge of each of a plurality of similar workpieces passed through saidrolling mill, said system comprising: means for determining a firstpredetermined relationship between the roll force of a selected rollstand during the passage of a present one of said workpieces throughsaid selected roll stand and a first average roll force of said selectedroll stand during the passage of previous similar workpieces throughsaid selected roll stand, means for determining a hardness correctionfactor in accordance with said first predetermined relationship, meansfor determining a second average roll force of one of said roll standsduring the passage of said plurality of workpieces through said one rollstand, and means for determining a corrected operation of said one rollstand in accordance with a second predetermined relationship betweensaid hardness correction factor and said second average roll force. 7.The gauge control system of claim 6 with said first predeterminedrelationship being (LOF(I)/ALOF(I)) where LOF(I) is the initial rollforce of said selected roll stand (I) in relation to said present oneworkpiece, and where ALOF(I) is the average roll force of said selectedroll stand (I) in relation to said previous similar workpieces.
 8. Thegauge control system of claim 6, with said first predeterminedrelationship being between the roll force LOF(I) of a selected rollstand (I) during the passage of said present one of said workpiecesthrough said selected roll stand (I) and a first average roll forceALOF(I) of said selected roll stand (I) during the passage of previoussimilar workpieces through said selected roll stand (I), with saidhardness correction factor FCF being determined in accordance with saidfirst predetermined relationship, and with said corrected operationCSD(N) of said one roll stand (N) being in accordance with a secondpredetermined relationship between said hardness correction factor FCFand a second average roll force ALOF(N).
 9. The gauge control system ofclaim 6, with said hardness correction factor FCF being determined bythe relationship FCF (LOF(I)/ALOF(I))-1 where LOF(I) is the initial rollforce of said selected roll stand (I) in relation to said present oneworkpiece, and where ALOF(I) is the average roll force of said selectedroll stand (I) in relation to said previous similar workpieces.
 10. Amethod of controlling the gauge of a plurality of similar workpiecespassed through a rolling mill having at least one roll stand, the stepsof said method comprising: determining a temperature change between thetemperature of a present workPiece and the average temperature of theprevious similar workpieces passed through said one roll stand,determining a temperature correction in relation to said change and apredetermined roll force relationship to said temperature change,determining the average roll force of said one roll stand during thepassage of said previous workpieces through that one roll stand, anddeterming a corrected operation of said one roll stand during thepassage of said present workpiece in accordance with said temperaturecorrection and said average roll force.
 11. The method of claim 10, withsaid determination of said temperature correction being in accordancewith TCF (ACST-CST) * TK where TCF is said temperature correction, whereACST is said average temperature, where CST is said temperature of apresent workpiece, and where TK is said predetermined roll forcerelationship to the temperature change.
 12. The method of controllingthe gauge of a plurality of similar workpieces of claim 10, with saidtemperature change (ACST-CST) being determined between the temperatureCST of a present workpiece and the average temperature ACST of theprevious similar workpieces passed through said one roll stand, withsaid temperature correction TCF being determined in relation to saidchange (ACST-CST) and a predetermined roll force relationship TK to saidtemperature change, and with said corrected operation CSD(N) of said oneroll stand (N) being determined during the passage of said presentworkpiece in accordance with said temperature correction TCF and saidaverage roll force ALOF(N).
 13. The method of claim 10, with saiddetermination of said temperature correction being in accordance withTCF ( ACST-CST) * TK where TCF is said temperature correction, whereACST is said average temperature, where CST is said temperature of thepresent workpiece, and where TK is said predetermined force relationshipto the temperature change, and with said corrected operation being inaccordance with CSD(N) SDREF(N) - ALOF(N) * TCF * K(N) where CSD(N) issaid corrected operation, SDREF(N) is the inital provided setting ofsaid roll stand (N), ALOF(N) is a predetermined roll force relationshipof said one roll stand (N), and K(N) is the mill spring modulus for saidone roll stand (N).
 14. A method of controlling the workpiece gaugeleaving a rolling mill having at least one roll stand operative toreduce the gauge of each of a plurality of similar workpieces passedthrough said rolling mill, the steps of said method comprising:establishing a first predetermined relationship between the roll forceof a selected roll stand during the passage of a present workpiece andthe average roll force of said selected roll stand during the passage ofprevious similar workpieces through said selected roll stand,establishing a hardness correction in relation to said firstpredetermined relationship, establishing the average roll force of atleast one roll stand during the passage of said previous workpiecesthrough said one roll stand, establishing a corrected operation of saidone roll stand in accordance with said hardness correction and saidaverage roll force, and controlling the operation of said one roll standin accordance with said corrected operation.
 15. The method of claim 14for controlling the workpiece gauge leaving a rolling mill having aplurality of roll stands, with said first predetermined relationshipbeing established between the roll force LOF(I) of a selected roll stand(I) during the passage of said present workpiece and the average rollforce ALOF(I) of said selected roll stand (I) during the passage ofprevious similar workpieces through said selected roll stand, with theaverage roll force ALOF(N) being established for at least one roll stand(N) during the passage of said previous workpieces through said one rollstand, with said corrected operation CSD(N) of at least said one rollstand (N) being established in accordance with the hardness correctionFCF and said average roll force ALOF(N), and with the operation of atleast said one roll stand (N) being controlled in accordance with therespective corrected operation CSD(N) of that roll stand.